DFT study for effects of hydrostatic pressure on structure, interaction and mechanical properties of CL-20/BTF cocrystal
Density functional theory (DFT) simulations were performed to study the effects of structure, interaction and mechanical properties of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/benzotrifuroxan (CL-20/BTF) under a hydrostatic pressure in the range of 0–100 GPa. The calculated structure agrees well with the experimental data at ambient pressure and 293 K. The CL-20/BTF cocrystal exhibits an anisotropic compression behavior, as shown by the change in lattice constants with pressure, because it is more difficult to compress along the b-axis. In addition, the band gap values decrease rapidly from 0 GPa to 40 Gpa and then decrease slowly with pressure increasing from 50 GPa to 100 GPa. Furthermore, the analysis of the active bond reveals that two types of O–N bonds in the furoxan group and four types of N–N bonds in CL-20 have significant responses to pressure. The Hirshfeld surface gives an insight into intermolecular interaction, and combining the analysis of the Hirshfeld surface and two-dimensional fingerprint plots shows that intermolecular interaction mainly comes from hydrogen bonding interactions and NO2–π interaction in CL-20/BTF cocrystal. According to the stronger intermolecular interaction (sum of O⋯H/H⋯O, N⋯H/H⋯N, O⋯N/N⋯O and O⋯O) decreasing with increasing pressure, it can be speculated that the impact sensitivity of CL-20/BTF increases as the pressure increases. The mechanical properties reveal that this cocrystal shows an increase in ductility, deformation resistance and stiffness with increasing pressure. The elastic anisotropy indicates that the CL-20/BTF varies anisotropically under pressure in the range of 0–100 GPa but is near isotropy level under 20 GPa.